In recent years, a white LED fabricated by combining a blue light-emitting diode, such as GaN, with a wavelength conversion member has come into widespread use. The wavelength conversion member is generally a phosphor particle, and a member obtained by dispersing phosphor particles in a resin is used. However, the wavelength conversion member obtained by dispersing phosphor particles in a resin has drawbacks, such as insufficient durability, due to heat resistance, etc., of the resin.
On the other hand, as in Patent Document 1, a wavelength conversion member obtained by dispersing a phosphor powder in glass has also been developed as the wavelength conversion member. Furthermore, as described in Patent Document 2, an attempt to use polycrystalline ceramics as the wavelength conversion member is also being made.
The wavelength conversion member obtained by dispersing a phosphor powder in glass or the polycrystalline ceramics phosphor material is an aluminum.garnet-based phosphor using Ce as an activator (YAG:Ce phosphor), and these techniques are related to developing a pseudo-white light-emitting device in which a blue emission color of a blue light-emitting diode and a yellow emission color of a YAG:Ce phosphor are combined.
In addition, with regard to a light-emitting device other than pseudo-white LED, as described in Patent Document 3, it is being attempted as well to use a semiconductor light-emitting element as the light source for a vehicular marker lamp, and a wavelength conversion member having an orange-to-red emission color is also required as the wavelength conversion member.
As disclosed in Patent Documents 4 and 5, using a phosphor material composed of polycrystalline ceramics as the wavelength conversion member having an orange-to-red emission color is also being attempted. However, whether the wavelength conversion members described in Patent Documents 4 and 5 have a luminescence intensity of a practical level and can achieve a wavelength control to obtain target chromaticity is unknown, and moreover, it is difficult to say that the production conditions are sufficiently studied.